Work will continue on various aspects of lymphocyte function. On the one hand, we will continue to seek rules that determine whether cell mediated immune reactions are effected directly via T lymphocytes or by an antibody directed cell dependent mechanism. In particular, we want to find out whether it is the amount or kind of cell surface antigen that makes this determination. Experiments continue on the ontogeny of immune responsiveness to mitogens and in the mixed lymphocyte reaction. Indications that a placental factor may inhibit these respones will be investigated. The overall goals continue to be the understanding of lymphocyte reaction in tumor and allograft immunity and the immune reactions in the maternal-fetal relation.